In utilizing geothermal energy for power the main problem is that the hot pressurized steam is accompanied by quantities of equally hot pressurized water that cannot be utilized efficiently in a steam turbine. Therefore the power plant is most efficient if the steam and water can be separated and discharged through different turbines designed particularly for water and steam respectively. The steam and water mixture may also carry solids and salts as well as corrosive gases causing excessive wear on the turbines as well as serious corrosion of major components of the power plant.
The radial outflow turbine, exemplified long ago by the Hero engine, in its modern conceptions has the drawbacks of capacity by reason of the limited nozzle arrangement, and low efficiency since the power fluid is accelerated circumferentially to the velocity of the rotor during its travel outwardly to the nozzles and no advantage is obtained from this acceleration. The high circumferential speed needed to obtain effective efficiencies in a reaction turbine results in a high power loss. These types of turbine also require a clean fluid as the power fluid to avoid damage to rotor and nozzles, and geothermal energy requires separation of the fluid before effective use in these devices.
The alternative to the Hero type of turbine is the multistage axial flow turbine. The required sophisticated installation in conjunction with the sophisticated turbine causes years of delay between conception and operation of this type of turbine in a geothermal power plant. This type of turbine has the particular objection of the risk of blading failures and of erosion resulting from the contaminated wet steam. The presence of large amounts of water in such turbines could be disastrous.